Knowledge of the mass of a motor vehicle is of elementary importance in order to enable optimum control of the shifting behavior of an automated transmission. Thus, the mass is needed for calculating the driving resistance, accurate determination of which is required for determining the shift speed at which the current gear, currently engaged, should be changed by a shift operation, and for determining the desired gear to which the transmission should be changed by the shift. For example, in the case of commercial vehicles whose mass can change markedly as a result of loading and unloading, the mass of the motor vehicle is also needed for determining the starting gear.
From EP 0 695 930 A1, a method for determining the mass or total weight of a motor vehicle is known. This known method relates to a motor vehicle whose drive train comprises an internal combustion engine provided with an electronic control system as the drive engine and a manual shift transmission. To determine the total weight of the motor vehicle, it is provided that at each of time points related to an upshift process, the torque of the drive engine and the longitudinal acceleration of the motor vehicle are determined, and the vehicle weight is calculated therefrom. The first values are preferably determined immediately before the engine clutch is engaged and the engine torque increased and the second values after the engine clutch has been completely engaged and the engine torque has been increased. To improve the accuracy of the total weight so determined, an average of several weight values is formed, each calculated from the same first values and from second values determined at various times. However, since in particular the time point when the first values are determined is chosen unfavorably because of the engaged synchronization and the engagement of the desired gear, the weight value so determined is relatively inaccurate.
Another method for determining the mass of a motor vehicle is the object of WO 00/11439. This method relates to a motor vehicles with an automated shift transmission in which the traction force is interrupted during a gearshift. The method provides that within a time window immediately before or after the gearshift several traction force values, i.e., force magnitudes, and in the traction-force-free phase during the shift operation at least two speed values, and accordingly movement magnitudes, are determined and a mass value is calculated from these. Since the mass value determined by this method can also be comparatively inaccurate, it is provided to form an average value from several mass values determined during a driving cycle.
A disadvantage of both known methods, apart from the inaccuracy of the weight or mass values determined, is also the fact that only one mass value can be determined at each shift operation so that to form an average value relatively many gearshifts and a correspondingly longer driving cycle time are required.
Thus, the purpose of the present invention is to propose a method whereby the mass of a motor vehicle can be determined more rapidly and with greater accuracy than has hitherto been possible.